Speaker make "pop" noise when pre amp turn off


Hi,
Does anyone have any idea what cause the speakers to make a "poping" sound when the pre amp is turn off?
Any remedies to this? It sounds fine when all the componet are on. The system does not have a hum problem. This only happen when the pre amp is turn off, or the amp turn off with the pre amp off?
Anyone has any idea?
Thanks.
gengisq
The correct sequence is...
ON: first - set preamp volume to minimum or muted
second - turn on preamp
third - turn on amp
OFF: first - set preamp volume to minimum or muted
second - turn off amp
third - turn off preamp
Alternative sequence:
set preamp volume to minimum when not listening, but always leave it ON. That's what I do.